To work at a job is to actively consent to that job.
It's hard to make an argument that you owe them notice if they didn't give notice of a significant change in working conditions.
We're not talking about coercion. Concealing the wages of other people in the organization is not coercion.
> You might think, “well, the employees should just get a different job then!”. But don't we want to fix the underlying problem instead of just churning our way through countless jobs?
No, we don't. The way we fix the problem is by choosing with whom we do business. "countless jobs" is a straw man.
The problem is, this often doesn't happen. The employee being paid too little (or working too long, or being otherwise treated poorly) might not know they are being coerced into this bad position, might not know how much their employer is hiding from them, may not want to go through the considerable effort of interviewing for another job, may not have the financial stability to put their family through that period of job hunting, or may just be of a non-contrarian disposition and enjoy having their stability in the current job.
There are a million reasons an employee would not respond to a blatant injustice by precisely identifying it and demanding it be righted or otherwise quitting. If you do do this, I truly think that is fantastic and I commend you. The ones who stay in these jobs, however, are being badly treated, at the employer's benefit. I don't think that's right, and I don't think they can be fully blamed, because a lot of these problems come from how adept the employer is at manipulating the situation. If you say “no, we don't want to fix that”, I'm sorry to say I can't agree with you.
I think this is missing the point. Do you think employers coercing employees into accepting conditions below what they should normally get is not a thing that happens? The employer, as opposed to the employee, has the power to manipulate the socioeconomic circumstances around the employee. They can (and do) prevent employees from discussing politics at the workplace or unionising, they can (and do) hide (and manipulate) information about who is getting paid what, they can (and do) decline additional compensation when it should be given (overtime), and this is the least of it.
You might think, “well, the employees should just get a different job then!”. But don't we want to fix the underlying problem instead of just churning our way through countless jobs? Sometimes it doesn't even work — you are often compelled to stay at a job for various reasons (you relocated with your family, you've worked there for a long time etc.), and you might not even realise this manipulation is happening to begin with.
The above comment said that employees will go very far to justify a raise. Don't you think that, if employees had all of the information their employers had, a lot of employees _would be_ able to justify a raise that they deserve, perhaps even without having previously realised this because of the information asymmetry? That sounds like an injustice to me.